Electroluminescent device

ABSTRACT

According to the invention there is provided an electroluminescent device comprising in sequence, an anode a layer of an electroluminescent material of general formula L(α) a M where M is a rare earth, lanthanide or an actinide, Lα is a organic complex and n is the valence state of M and a cathode, in which the layer of an electroluminescent material includes a fluorescent dye.

The present invention relates to electroluminescent devices anddisplays.

Materials which emit light when an electric current is passed throughthem are well known and used in a wide range of display applications.Liquid crystal devices and devices which are based on inorganicsemiconductor systems are widely used, however these suffer from thedisadvantages of high energy consumption, high cost of manufacture, lowquantum efficiency and the inability to make flat panel displays.

With organic light emitting polymers it is not possible to obtain purecolours, they are expensive to make and have a relatively lowefficiency.

Patent application WO98/58037 describes a range of lanthanide complexeswhich can be used in electroluminescent devices which have improvedproperties and give better results. Patent Applications PCT/GB99/01773,PCT/GB99/03619, PCT/GB99/04030, PCT/GB99/04024, PCT/GB99/04028,PCT/GB00/00268 describe electroluminescent complexes, structures anddevices using rare earth chelates.

In order to modify the light emitted a fluorescent dye can beincorporated in the electroluminescent layer or in the electrontransmitting layer.

According to the invention there is provided an electroluminescentdevice comprising in sequence, an anode, a layer of anelectroluminescent material of general formula (Lα)_(n)M where M is arare earth, lanthanide or an actinide, Lα is an organic complex and n isthe valence state of M and a cathode, in which the layer of anelectroluminescent material includes a fluorescent dye.

The electroluminescent compounds which can be used as theelectroluminescent materials in the present invention are of generalformula (Lα)_(n)M where M is a rare earth, lanthanide or an actinide, Lαis an organic complex and n is the valence state of M.

Preferred electroluminescent compounds which can be used in the presentinvention are of formula

where Lα and Lp are organic ligands, M is a rare earth, transitionmetal, lanthanide or an actinide and n is the valence state of the metalM. The ligands Lα can be the same or different and there can be aplurality of ligands Lp which can be the same or different.

For example (L₁)(L₂)(L₃)(L . . . )M (Lp) where M is a rare earth,transition metal, lanthanide or an actinide and (L₁)(L₂)(L₃)(L . . . )are the same or different organic complexes and (Lp) is a neutralligand. The total charge of the ligands (L₁)(L₂)(L₃)(L . . . ) is equalto the valence state of the metal M. Where there are 3 groups Lα whichcorresponds to the m valence state of M the complex has the formula(L₁)(L₂)(L₃)M (Lp) and the different groups (L₁)(L₂)(L₃) may be the sameor different

Lp can be monodentate, bidentate or polydentate and there can be one ormore ligands Lp.

Preferably M is metal ion having an unfilled inner shell and thepreferred metals are selected from Sm(III), Eu(II), Eu(III), Tb(III),Dy(III), Yb(III), Lu(III), Gd (III), Gd(III) U(III), Tm(III), Ce (III),Pr(III), Nd(III), Pm(III), Dy(III), Ho(III), Er(III) and more preferablyEu(III), Tb(III), Dy(III), Gd (IlI).

Further electroluminescent compounds which can be used in the presentinvention are of general formula (Lα)_(n)M₁M₂ where M₁ is the same as Mabove, M₂ is a non rare earth metal, Lα is a as above and n is thecombined valence state of M₁ and M₂. The complex can also comprise oneor more neutral ligands Lp so the complex has the general formula(Lα)_(n) M₁ M₂ (Lp), where Lp is as above. The metal M₂ can be any metalwhich is not a rare earth, transition metal, lanthanide or an actinideexamples of metals which can be used include lithium, sodium, potassium,rubidium, caesium, beryllium, magnesium, calcium, strontium, barium,copper (I), copper (II), silver, gold, zinc, cadmium, boron, aluminium,gallium, indium, germanium, tin (II), tin (IV), antimony (II), antimony(IV), lead (II), lead (IV) and metals of the first, second and thirdgroups of transition metals in different valence states e.g. manganese,iron, ruthenium, osmium, cobalt, nickel, palladium(II), palladium(IV),platinum(II), platinum(IV), cadmium, chromium. titanium, vanadium,zirconium, tantulum, molybdenum, rhodium, iridium, titanium, niobium,scandium, yttrium.

For example (L₁)(L₂)(L₃)(L . . . )M (Lp) where M is a rare earth,transition metal, lanthanide or an actinide and (L₁)(L₂)(L₃)(L . . . )and (Lp) are the same or different organic complexes.

Further organometallic complexes which can be used in the presentinvention are binuclear, trinuclear and polynuclear organometalliccomplexes e.g. of formula(Lm)_(x)M₁←M₂(Ln)_(y) e.g.

where L is a bridging ligand and where M₁ is a rare earth metal and M₂is M₁ or a non rare earth metal, Lm and Ln are the same or differentorganic ligands Lα as defined above, x is the valence state of M₁ and yis the valence state of M₂.

In these complexes there can be a metal to metal bond or there can beone or more bridging ligands between M₁ and M₂ and the groups Lm and Lncan be the same or different.

By trinuclear is meant there are three rare earth metals joined by ametal to metal bond i.e. of formula

where M₁, M₂ and M₃ are the same or different rare earth metals and Lm,Ln and Lp are organic ligands Lα and x is the valence state of M₁, y isthe valence state of M₂ and z is the valence state of M₃. Lp can be thesame as Lm and Ln or different.

The rare earth metals and the non rare earth metals can be joinedtogether by a metal to metal bond and/or via an intermediate bridgingatom, ligand or molecular group. For example the metals can be linked bybridging ligands e.g.

where L is a bridging ligand

By polynuclear is meant there are more than three metals joined by metalto metal bonds and/or via intermediate ligands

where M₁, M₂, M₃ and M₄ are rare earth metals and L is a bridgingligand.

The metal M₂ can be any metal which is not a rare earth, transitionmetal, lanthanide or an actinide examples of metals which can be usedinclude lithium, sodium, potassium, rubidium, caesium, beryllium,magnesium, calcium, strontium, barium, copper, silver, gold, zinc,cadmium, boron, aluminium, gallium, indium, germanium, tin, antimony,lead, and metals of the first, second and third groups of transitionmetals e.g. manganese, iron, ruthenium, osmium, cobalt, nickel,palladium, platinum, cadmium, chromium. titanium, vanadium, zirconium,tantulum, molybdenum, rhodium, iridium, titanium, niobium, scandium,yttrium etc.

Preferably Lα is selected from β diketones such as those of formulae

where R₁, R₂ and R₃ can be the same or different and are selected fromhydrogen, and substituted and unsubstituted hydrocarbyl groups such assubstituted and unsubstituted aliphatic groups, substituted andunsubstituted aromatic, heterocyclic and polycyclic ring structures,fluorocarbons such as trifluoryl methyl groups, halogens such asfluorine or thiophenyl groups; R₁, R₂ and R₃ can also form substitutedand unsubstituted fused aromatic, heterocyclic and polycyclic ringstructures and can be copolymerisable with a monomer e.g. styrene. X isSe, S or O, Y can be hydrogen, substituted or unsubstituted hydrocarbylgroups, such as substituted and unsubstituted aromatic, heterocyclic andpolycyclic ring structures, fluorine, fluorocarbons such as trifluorylmethyl groups, halogens such as fluorine or thiophenyl groups ornitrile.

Examples of R₁ and/or R₂ and/or R₃ include aliphatic, aromatic andheterocyclic alkoxy, aryloxy and carboxy groups, substituted andsubstituted phenyl, fluorophenyl, biphenyl, phenanthrene, anthracene,naphthyl and fluorene groups alkyl groups such as t-butyl, heterocyclicgroups such as carbazole.

Some of the different groups L may also be the same or different chargedgroups such as carboxylate groups so that the group L₁ can be as definedabove and the groups L₂, L₃ . . . can be charged groups such as

where R is R₁ as defined above or the groups L₁, L₂ can be as definedabove and L₃ . . . etc. are other charged groups.

R₁, R₂ and R₃ can also be

where X is O, S, Se or NH.

A preferred moiety R₁ is trifluoromethyl CF₃ and examples of suchdiketones are, banzoyltrifluoroacetone, p-chlorobenzoyltrifluoroacetone,p-bromotrifluoroacetone, p-phenyltrifiuoroacetone,1-naphthoyltrifluoroacetone, 2-naphthoyltrifluoroacetone,2-phenathoyltrifluoroacetone, 3-phenanthoyltrifluoroacetone,9-anthroyltrifluoroacetonetrifluoroacetone, cinnamoyltrifluoroacetone,and 2-thenoyltrifluoroacetone.

The different groups L may be the same or different ligands of formulae

where X is O, S, or Se and R₁ R₂ and R₃ are as above

The different groups L may be the same or different quinolatederivatives such as

where R is hydrocarbyl, aliphatic, aromatic or heterocyclic carboxy,aryloxy, hydroxy or alkoxy e.g. the 8 hydroxy quinolate derivatives or

where R, R₁, and R₂ are as above or are H or F e.g. R₁ and R₂ are alkylor alkoxy groups

As stated above the different groups L may also be the same or differentcarboxylate groups e.g.

where R₅ is a substituted or unsubstituted aromatic, polycyclic orheterocyclic ring a polypyridyl group, R₅ can also be a 2-ethyl hexylgroup so L_(n) is 2-ethylhexanoate or R₅ can be a chair structure sothat L_(n) is 2-acetyl cyclohexanoate or Lα can be

where R is as above e.g. alkyl, allenyl, amino or a fuised ring such asa cyclic or polycyclic ring.

The different groups L may also be

Where R, R₁ and R₂ are as above or

The groups L_(P) can be selected from

Where each Ph which can be the same or different and can be a phenyl(OPNP) or a substituted phenyl group, other substituted or unsubstitutedaromatic group, a substituted of unsubstituted heterocyclic orpolycyclic group, a substituted or unsubstituted fuised aromatic groupsuch as a naphthyl, anthracene, phenanthrene or pyrene group. Thesubstituents can be for example an alkyl, aralkyl, alkoxy, aromatic,heterocyclic, polycyclic group, halogen such as fluorine, cyano, amino.Substituted amino etc. Examples are given in FIGS. 1 and 2 of thedrawings where R, R₁, R₂, R₃ and R₄ can be the same or different and areselected from hydrogen, hydrocarbyl groups, substituted andunsubstituted aromatic, heterocyclic and polycyclic ring structures,fluorocarbons such as trffluoryl methyl groups, halogens such asfluorine or thiophenyl groups; R, R₁, R₂, R₃ and R₄ can also formsubstituted and unsubstituted fuised aromatic, heterocyclic andpolycyclic ring structures and can be copolymerisable with a monomere.g. styrene. R, R₁, R₂, R₃ and R₄ can also be unsaturated alklenegroups such as vinyl groups or groups—C—CH₂═CH₂—Rwhere R is as above.

L_(p) can also be compounds of formulae

where R₁, R₂ and R₃ are as referred to above, for example bathophenshown in FIG. 3 of the drawings in which R is as above or

where R₁, R₂ and R₃ are as referred to above.

L_(p) can also be

where Ph is as above.

Other examples of L_(p) chelates are as shown in FIG. 4 and fluorene andfluorene derivatives e.g. a shown in FIG. 5 and compounds of formulae asshown as shown in FIGS. 6 to 8.

Specific examples of Lα and Lp are tripyridyl and TMHD, and TMMDcomplexes, α, α′, α″ tripyridyl, crown ethers, cyclans, cryptansphthalocyanans, porphoryins ethylene diamine tetramine (EDTA), DCTA,DTPA and TTHA. Where TMHD is 2,2,6,6-tetramethyl-3,5-heptanedionato andOPNP is diphenylphosphonimide triphenyl phosphorane. The formulae of thepolyamines are shown in FIG. 11.

Other electroluminescent materials which can be used include metalquinolates such as lithium quinolate, and non rare earth metal complexessuch as aluminium, magnesium, zinc and scandium complexes such ascomplexes of β-diketones e.g. Tris-(1,3-diphenyl-1-3-propanedione) (DBM)and suitable metal complexes are Al(DBM)₃, Zn(DBM)₂ and Mg(DBM)₂,Sc(DBM)₃ etc.

The first electrode is preferably a transparent substrate such as is aconductive glass or plastic material which acts as the anode, preferredsubstrates are conductive glasses such as indium tin oxide coated glass,but any glass which is conductive or has a conductive layer such as ametal or conductive polymer can be used. Conductive polymers andconductive polymer coated glass or plastics materials can also be usedas the substrate.

The hole transporting material can be an amine complex such as poly(vinylcarbazole),N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine(TPD),an unsubstituted or substituted polymer of an amino substituted aromaticcompound, a polyaniline, substituted polyanilines, polytiiophenes,substituted polythiophenes, polysilanes etc. Examples of polyanilinesare polymers of

where R is in the ortho- or meta-position and is hydrogen, C1-18 alkyl,C1-6 alkoxy, amino, chloro, bromo, hydroxy or the group

where R is alky or aryl and R′ is hydrogen, C1-6 alkyl or aryl with atleast one other monomer of formula I above.

Or the hole transporting material can be a polyaniline, polyanilineswhich can be used in the present invention have the general formula

where p is from 1 to 10 and n is from 1 to 20, R is as defined above andX is an anion, preferably selected from Cl, Br, SO₄, BF₄, PF₆, H₂PO₃,H₂PO₄, arylsulphonate, arenedicarboxylate, polystyrenesulphonate,polyacrylate alkysulphonate, vinylsulphonate, vinylbenzene sulphonate,cellulose sulphonate, camphor sulphonates, cellulose sulphate or aperfluorinated polyanion.

Examples of arylsulphonates are p-toluenesulphonate, benzenesulphonate,9,10-anthraquinone-sulphonate and anthracenesulphonate, an example of anarenedicarboxylate is phthalate and an example of arenecarboxylate isbenzoate.

We have found that protonated polymers of the unsubstituted orsubstituted polymer of an amino substituted aromatic compound such as apolyaniline are difficult to evaporate or cannot be evaporated, howeverwe have surprisingly found that if the unsubstituted or substitutedpolymer of an amino substituted aromatic compound is deprotonated the itcan be easily evaporated i.e. the polymer is evaporable.

Preferably evaporable deprotonated polymers of unsubstituted orsubstituted polymer of an amino substituted aromatic compound are used.The de-protonated unsubstituted or substituted polymer of an aminosubstituted aromatic compound can be formed by deprotonating the polymerby treatment with an alkali such as ammonium hydroxide or an alkalimetal hydroxide such as sodium hydroxide or potassium hydroxide.

The degree of protonation can be controlled by forming a protonatedpolyaniline and de-protonating. Methods of preparing polyanilines aredescribed in the article by A. G. MacDiarinid and A. F. Epstein, FaradayDiscussions, Chem Soc. 88 P 319 1989.

The conductivity of the polyaniline is dependant on the degree ofprotonation with the maximum conductivity being when the degree ofprotonation is between 40 and 60% e.g. about 50% for example.

Preferably the polymer is substantially fully deprotonated

A polyaniline can be formed of octamer units i.e. p is four e.g.

The polyanilines can have conductivities of the order of 1×10⁻¹ Siemencm⁻¹ or higher.

The aromatic rings can be unsubstituted or substituted e.g. by a C1 to20 alkyl group such as ethyl.

The polyaniline can be a copolymer of aniline and preferred copolymersare the copolymers of aniline with o-anisidine, m-sulphanilic acid oro-aminophenol, or o-toluidine with o-aminophenol, o-ethylaniline,o-phenylene diamine or with amino anthracenes.

Other polymers of an amino substituted aromatic compound which can beused include substituted or unsubstituted polyarninonapthatenes,polyaminoanthracenes, potyaminophenanthrenes, etc. and polymers of anyother condensed polyaromatic compound. Polyaminoanthracenes and methodsof making them are disclosed in U.S. Pat. No. 6,153,726. The aromaticrings can be unsubstituted or substituted e.g. by a group R as definedabove.

Other hole transporting materials are conjugated polymer and theconjugated polymers which can be used can be any of the conjugatedpolymers disclosed or referred to in U.S. Pat. No. 5,807,627,PCT/WO90/13148 and PCT/WO92/03490.

The preferred conjugated polymers are poly(p-phenylenevinylene)-PPV andcopolymers including PPV. Other preferred polymers are poly(2,5dialkoxyphenylene vinylene) such aspoly(2-methoxy-5-(2-methoxypentyloxy-1,4-phenylene vinylene),poly(2-methoxypentyloxy)-1,4-phenylenevinylene),poly(2-methoxy-5-(2-dodecyloxy-1,4-phenylenevinylene) and other poly(2,5dialkoxyphenylenevinylenes) with at least one of the alkoxy groups beinga long chain solubilising alkoxy group, poly fluorenes andoligofluorenes, polyphenylenes and oligophenylenes, polyanthracenes andoligo anthracenes, ploythiophenes and oligothiophenes.

In PPV the phenylene ring may optionally carry one or more substituentse.g. each independently selected from alkyl, preferably methyl, alkoxy,preferably methoxy or ethoxy.

Any poly(arylenevinylene) including substituted derivatives thereof canbe used and the phenylene ring in poly(p-phenylenevinylene) may bereplaced by a fused ring system such as anthracene or naphthlyene ringand the number of vinylene groups in each polyphenylenevinylene moietycan be increased e.g. up to 7 or higher.

The conjugated polymers can be made by the methods disclosed in U.S.Pat. No. 5,807,627, PCT/WO90113148 and PCT/WO92/03490.

The thickness of the hole transporting layer is preferably 20 nm to 200nm.

The polymers of an amino substituted aromatic compound such aspolyanilines referred to above can also be used as buffer layers with orin conjunction with other hole transporting materials.

The structural formulae of some other hole trsporting materials areshown in FIGS. 12, 13, 14 15 and 16 of the drawings, where R₁, R₂ and R₃can be the same or different and are selected from hydrogen, andsubstituted and unsubstituted hydrocarbyl groups such as substituted andunsubstituted aliphatic groups, substituted and unsubstituted aromatic,heterocyclic and polycyclic ring structures, fluorocarbons such astrifluoryl methyl groups, halogens such as fluorine or thiophenylgroups; R₁, R₂ and R₃ can also form substituted and unsubstituted fusedaromatic, heterocyclic and polycyclic ring structures and can becopolymerisable with a monomer e.g. styrene. X is Se, S or O, Y can behydrogen, substituted or unsubstituted hydrocarbyl groups, such assubstituted and unsubstituted aromatic, heterocyclic and polycyclic ringstructures, fluorine, fluorocarbons such as trifluoryl methyl groups,halogens such as fluorine or thiophenyl groups or nitrile.

Examples of R₁ and/or R₂ and/or R₃ include aliphatic, aromatic andheterocyclic alkoxy, aryloxy and carboxy groups, substituted andsubstituted phenyl, fluorophenyl, biphenyl, phenanthrene, anthracene,naphthyl and fluorene groups alkyl groups such as t-butyl, heterocyclicgroups such as carbazole.

Optionally there is a layer of an electron injecting material betweenthe cathode and the electroluminescent material layer, the electroninjecting material is a material which will transport electrons when anelectric current is passed through electron injecting materials includea metal complex such as a metal quinolate e.g. an aluminium quinolate,lithium quinolate, a cyano anthracene such as 9,10 dicyano anthracene,cyano substituted aromatic compounds, tetracyanoquinidodimethane apolystyrene sulphonate or a compound with the structural formulae shownin FIGS. 9 and 10 of the drawings in which the phenyl rings can besubstituted with substituents R as defined above. Instead of being aseparate layer the electron injecting material can be mixed with theelectroluminescent material and co-deposited with it.

The second electrode fumctions as the cathode and can be any low workfunction metal e.g. aluminium, calcium, lithium, silver/magnesiumalloys, rare earth metal alloys etc., aluminium is a preferred metal. Ametal fluoride such as an allali metal, rare earth metal or their alloyscan be used as the second electrode for example by having a metalfluoride layer formed on a metal.

Optionally the hole transporting material can be mixed with theelectroluminescent material and co-deposited with it.

The hole transporting materials, the electroluminescent material and theelectron injecting materials can be mixed together to form one layer,which simplifies the construction.

The display of the invention may be monochromatic or polychromatic.Electroluminescent rare earth chelate compounds are known which willemit a range of colours e.g. red, green, and blue light and white lightand examples are disclosed in Patent Applications WO98/58037PCT/GB98/01773, PCT/GB99/03619, PCT/GB99/04030, PCT/GB99/04024,PCTVGB99/04028, PCT/GB00/00268 and can be used to form OLEDs emittingthose colours. Thus, a full colour display can be formed by arrangingthree individual backplanes, each emitting a different primarymonochrome colour, on different sides of an optical system, from anotherside of which a combined colour image can be viewed. Alternatively, rareearth chelate electroluminescent compounds emitting different colourscan be fabricated so that adjacent diode pixels in groups of threeneighbouring pixels produce red, green and blue light. In a flirteralternative, field sequential colour filters can be fitted to a whitelight emitting display.

Either or both electrodes can be formed of silicon and theelectroluminescent material and intervening layers of a holetransporting and electron transporting materials can be formed as pixelson the silicon substrate. Preferably each pixel comprises at least onelayer of a rare earth chelate electroluminescent material and an (atleast semi-) transparent electrode in contact with the organic layer ona side thereof remote from the substrate.

Preferably, the substrate is of crystalline silicon and the surface ofthe substrate may be polished or smoothed to produce a flat surfaceprior to the deposition of electrode, or electroluminescent compound.Alternatively a non-planarised silicon substrate can be coated with alayer of conducting polymer to provide a smooth, flat surface prior todeposition of further materials.

In one embodiment, each pixel comprises a metal electrode in contactwith the substrate. Depending on the relative work functions of themetal and transparent electrodes, either may serve as the anode with theother constituting the cathode.

When the silicon substrate is the cathode an indium tin oxide coatedglass can act as the anode and light is emitted through the anode. Whenthe silicon substrate acts as the anode the cathode can be formed of atransparent electrode which has a suitable work fumction, for example bya indium zinc oxide coated glass in which the indium zinc oxide has alow work function. The anode can have a transparent coating of a metalformed on it to give a suitable work function. These devices aresometimes referred to as top emitting devices or back emitting devices.

The metal electrode may consist of a plurality of metal layers, forexample a higher work function metal such as aluminium deposited on thesubstrate and a lower work fuiction metal such as calcium deposited onthe higher work function metal. In another example, a further layer ofconducting polymer lies on top of a stable metal such as aluminium.

Preferably, the electrode also acts as a mirror behind each pixel and iseither deposited on, or sunk into, the planarised surface of thesubstrate. However, there may alternatively be a light absorbing blacklayer adjacent to the substrate.

In still another embodiment, selective regions of a bottom conductingpolymer layer are made non-conducting by exposure to a suitable aqueoussolution allowing formation of arrays of conducting pixel pads whichserve as the bottom contacts of the pixel electrodes.

As described in WO00/60669 the brightness of light emitted from eachpixel is preferably controllable in an analogue manner by adjusting thevoltage or current applied by the matrix circuitry or by inputting adigital signal which is converted to an analogue signal in each pixelcircuit. The substrate preferably also provides data drivers, dataconverters and scan drivers for processing information to address thearray of pixels so as to create images. When an electroluminescentmaterial is used which emits light of a different colour depending onthe applied voltage the colour of each pixel can be controlled by thematrix circuitry.

In one embodiment, each pixel is controlled by a switch comprising avoltage controlled element and a variable resistance element, both ofwhich are conveniently formed by metal-oxide-semiconductor field effecttransistors (MOSFETs) or by an active matrix transistor.

U.S. Pat. No. 4,769,292 disclose a range of fluorescent dyes which canbe used in luminescent devices in which the electroluminescent materialis aluminium quinolate or an aluminium quinolate derivative.

We have now discovered that fluorescent dyes can be added toelectroluminescent complexes of general formula (Lα)_(n)M where M is arare earth, lanthanide or an actinide, Lα is an organic complex and n isthe valence state of M.

As explained in U.S. Pat. No. 4,769,292 the light is emitted in theelectroluminescent material layer in response to the injection andcombination of holes in the layer. If a fluorescent material is added tothe electroluminescent the colour of the emitted light can be varied. Intheory, if an electroluminescent host material and a fluorescentmaterial could be found for blending which have exactly the sameaffinity for hole-electron recombination each material should emit lightupon injection of holes and electrons in the luminescent zone. Theperceived hue of light emission would be the visual integration of bothemissions. Since imposing such a balance of host and fluorescentmaterials is highly limiting, it is preferred to choose the fluorescentmaterial so that it provides the favored sites for light emission. Whenonly a small proportion of fluorescent material providing favored sitesfor light emission is present, peak intensity wavelength emissionstypical of the host material can be entirely eliminated in favor of anew peak intensity wavelength emission attributable to the fluorescentmaterial. While the minimum proportion of fluorescent materialsufficient to achieve this effect varies by the specific choice of hostand fluorescent materials, in no instance is it necessary to employ morethan about 10 mole percent fluorescent material, based on moles of hostmaterial and seldom is it necessary to employ more than 1 mole percentof the fluorescent material. On the other hand, for any host materialcapable of emitting light in the absence of fluorescent material,limiting the fluorescent material present to extremely small amounts,typically less than about 10⁻³ mole percent, based on host material, canresult in retaining emission at wavelengths characteristic of the hostmaterial. Thus, by choosing the proportion of a fluorescent materialcapable of providing favored sites for light emission, either a full orpartial shifting of emission wavelengths can be realized. This allowsthe spectral emissions of the EL devices of this invention to beselected and balanced to suit the application to be served.

Choosing fluorescent materials capable of providing favored sites forlight emission necessarily involves relating the properties of thefluorescent material to those of the host material. The host materialcan be viewed as a collector for injected holes and electrons with thefluorescent material providing the molecular sites for light emission.One important relationship for choosing a fluorescent material capableof modifying the hue of light emission when present in a host materialis a comparison of the reduction potentials of the two materials. Thefluorescent materials demonstrated to shift the wavelength of lightemission have exhibited a less negative reduction potential than that ofthe host material.

Reduction potentials, measured in electron volts, have been widelyreported in the literature along with varied techniques for theirmeasurement. Since it is a comparison of reduction potentials ratherthan their absolute values which is desired, it is apparent that anyaccepted technique for reduction potential measurement can be employed,provided both the fluorescent and host material reduction potentials aresimilarly measured. A preferred oxidation and reduction potentialmeasurement techniques is reported by R. J. Cox, PhotographicSensitivity, Academic Press, 1973, Chapter 15.

A second important relationship for choosing a fluorescent materialcapable of modifying the hue of light emission when present in a hostmaterial is a comparison of the bandgap potentials of the two materials.The fluorescent materials demonstrated to shift the wavelength of lightemission have exhibited a lower bandgap potential than that of the hostmaterial. The bandgap potential of a molecule is taken as the potentialdifference in electron volts (eV) separating its ground state and firstsinglet state. Bandgap potentials and techniques for their measurementhave been widely reported in the literature. The bandgap potentialsherein reported are those measured in electron volts (eV) at anabsorption wavelength which is bathochromic to the absorption peak andof a magnitude one tenth that of the magnitude of the absorption peak.Since it is a comparison of bandgap potentials rather than theirabsolute values which is desired, it is apparent that any acceptedtechnique for bandgap measurement can be employed, provided both thefluorescent and host material band gaps are similarly measured.

One illustrative measurement technique is disclosed by F. Gutman and L.E. Lyons, Organic Semiconductors, Wiley, 1967, Chapter 5. Where a hostmaterial is chosen which is itself capable of emitting light in theabsence of the fluorescent material, it has been observed thatsuppression of light emission at the wavelengths of emissioncharacteristics of the host material alone and enhancement of emissionat wavelengths characteristic of the fluorescent material occurs whenspectral coupling of the host and fluorescent materials is achieved. Byspectral coupling it is meant that an overlap exists between thewavelengths of emission characteristic of the host material alone andthe wavelengths of light absorption of the fluorescent material in theabsence of the host material. Optimal spectral coupling occurs when themaximum emission of the host material alone substantially matches within±25 nm the maximum absorption of the fluorescent material alone.

In practice advantageous spectral coupling can occur with peak emissionand absorption wavelengths differing by up to 100 nm or more, dependingon the width of the peaks and their hypsochromic and bathochromicslopes. Where less than optimum spectral coupling between the host andfluorescent materials is contemplated, a bathochromic as compared to ahypsochromic displacement of the fluorescent material produces moreefficient results.

Useful fluorescent materials are those capable of being blended with thehost material and fabricated into thin films satisfying the thicknessranges described above forming the luminescent zones of the EL devicesof this invention. While crystalline host materials do not lendthemselves to thin film formation, the limited amounts of fluorescentmaterials present in the host materials permits the use of fluorescentmaterials which are alone incapable of thin film formation.

Preferred fluorescent materials are those which form a common phase withthe host material.

Fluorescent dyes constitute a preferred class of fluorescent materials,since dyes lend themselves to molecular level distribution in the hostmaterial. Although any convenient technique for dispersing thefluorescent dyes in the host materials can be undertaken, preferredfluorescent dyes are those which can be vacuum vapour deposited alongwith the host materials.

Assuming other criteria, noted above, are satisfied, fluorescent laserdyes are recognized to be particularly useful fluorescent materials foruse in the organic EL devices of this invention. One preferred class offluorescent dyes are fluorescent coumarin dyes. Among specificallypreferred fluorescent coumarin dyes as described in U.S. Pat. No.4,769,292 the contents of which are hereby incorporated by reference.

Another preferred class of fluorescent dyes are fluorescent4-dicyanomethylene-4H-pyrans and 4-dicyanomethylene-4H-thiopyrans,hereinafter referred to as fluorescent dicyanomethylenepyran andthiopyran dyes the preferred fluorescent dyes of this class arespecified in U.S. Pat. No. 4,769,292. Useful fluorescent dyes can alsobe selected from among known polymethine dyes, which include thecyanines, merocyanines, complex cyanines and merocyanines (i.e., tri-,tetra and poly-nuclear cyanines and merocyanines}, oxonols, hemioxonols,styryls, merostyryls, and streptocyanines.

The cyanine dyes include, joined by a methine linkage, two basicheterocyclic nuclei, such as azolium or azinium nuclei, for example,those derived from pyridinium, quinolinium, isoquinolinium, oxazolium,thiazolium, selenazolium, indazolium, pyrazolium, pyrrolium, indoliurn,3H-indolium, imidazolium, oxadiazolium, thiadioxazolium, benzoxazolium,benzothiazolium, benzoselenazolium, benzotellurazolium, benzimidazolium,3H or 1H-benzoindolium, naphthoxazolium, naphthothiazolium,naphthoselenazolium, naphthotellurazolium, carbazolium,pyrrolopyridinium, phenanthrothiazolium, and acenaphthothiazoliumquaternary salts.

Cyanine dyes can contain two heterocyclic nuclei joined by a methinelinkage containing an uneven number of methine groups or can contain aheterocyclic nucleus joined by a methine linkage containing an evennumber of methine groups.

The greater the number of the methine groups linking nuclei in thepolymethine dyes in general and the cyanine dyes in particular thelonger the absorption wavelengths of the dyes. For example,dicarbocyanine dyes (cyanine dyes containing five methine groups linkingtwo basic heterocyclic nuclei) exhibit longer absorption wavelengthsthan carbocyanine dyes (cyanine dyes containing three methine groupslinking two basic heterocyclic nuclei) which in turn exhibit longerabsorption wavelengths than simple cyanine dyes (cyanine dyes containinga single methine group linking two basic heterocyclic nuclei).Carbocyanine and dicarbocyanine dyes are longer wavelength dyes whilesimple cyanine dyes are typically yellow dyes, but can exhibitabsorption maxima up to about 550 nm in wavelength with proper choice ofnuclei and other components capable of bathochromically shiftingabsorption. Preferred polymethine dyes, particularly cyanine dyes, foruse as fluorescent dyes are so-called rigidized dyes. These dyes areconstructed to restrict the movement of one nucleus in relation toanother. This avoids rddiationless, kinetic dissipation of the excitedstate energy. One approach to rigidizing the dye structure is toincorporate a separate bridging group providing a separate linkage inaddition to the methine chain linkage joining the terminal nuclei of thedye. Bridged polymethine dyes are illustrated by Brooker et al U.S. Pat.No. 2,478,367, Brooker U.S. Pat. No. 2,479,152, Gilbert U.S. Pat. No.4,490,463, and Tredwell et al, “Picosecond Time Resolved FluorescenceLifetimes of the Polymethine and Related Dyes”, Chemical Physics, Vol.43 (1979) pp. 307-316. The methine chain joining polymethine dye nucleican be rigidized by including the methine chain as part of a cyclicnucleus joining the terminal basic nuclei of the dye. One of thetechniques for both rigidizing and bathochromically shifting theabsorption maxima of polymethine dyes in general and cyanine dyes inparticular is to include in the methine linkage an oxocarbon bridgingnucleus

Another useful class of fluorescent dyes are 4-oxo4H-benz-[d,e]anthracenes, hereinafter referred to as oxobenzanthracene dyes.

Dyes of this class and their preparations are disclosed in Goswami et alU.S. Ser. No. 824,765, filed Jan. 31, 1986, commonly assigned, titledFluorescent Dyes and Biological and Analytical uses thereof.

The oxobenzanthracene dyes can be prepared by known methods e.g. (1)preparation of a dihydrophenalenone by the procedure described by Cookeet al, Australian J. Chem., 11, pp. 230-235 (1958), (2) preparation ofthe lithium enolate of the dihydrophenalenone, (3) reaction of thelithium enolate with the appropriate phosphonium iodide reagent, and (4)reaction of this product with cupric chloride and lithium chloride toproduce the chlorinated or unchlorinated dye.

The oxobenzanthracene can have one or more substituents in the structureas long as the substituents do not adversely affect the fluorescence ofthe compound, such as alkyl (e.g., alkyl of 1 to 5 carbon atoms), aryl(e.g., phenyl), and other groups.

Another useful class of fluorescent dyes are xanthene dyes. Oneparticularly preferred class of xanthene dyes are rhodamine dyes.

Another specifically preferred class of xanthene dyes are fluoresceindyes

Another useful group of fluorescent dyes are pyrylium, thiapyrylium,selenapyrylium, and telluropyrylium dyes. Dyes from the first three ofthese classes are disclosed by Light U.S. Pat. No. 3,615,414 while dyesof the latter class are disclosed by Detty U.S. Pat. No. 4,584,258, thedisclosures of which are here incorporated by reference. Since thelatter two classes of dyes are bathochromically shifted toward theinfrared the former two classes of dyes are preferred for achievingvisible light emissions.

Another useful class of fluorescent dyes are fluorescent carbostyrildyes. These dyes are characterized by a 2-quinolinol or isoquinolinolring structure, often fused with other rings. The wavelength of maximumfluorescence generally increases with the presence of other fused rings.

Examples of more complex fused ring carbostyril dyes are provided byKadhim and Peters, “New Intermediates and Dyes for Synthetic PolymerFibres Substituted Benzimidazolothioxanthenoisoquinolines for PolyesterFibres”, JSDC, June 1974, pp. 199-201, and Arient et al, “Imidazole DyesXX-Colouring Properties of 1,2-Napthooxylenebenzimidazole Derivatives”,JSDC, June 1968, pp. 246-251.

Among other fused ring fluorescent dyes the perylene dyes, characterizedby a dinapthylene nucleus. A variety of useful fluorescent perylene dyesare known, such as, for example those disclosed by Rademacher et al,“Soluble Perylene Fluorescent Dyes with Photostability”, Chem. Ber. ,Voi. 115, pp. 2927-2934, 1982, and European Patent Application No.553,363A 1, published Jul. 7, 1982.

Many other classes of known fluorescent dyes, such as acridine dyes;bis(styryl)benzene dyes; pyrene dyes; oxazine dyes; and phenyleneoxidedyes, sometimes referred to as POPOP dyes; are useful.

Not only are there many available classes of fluorescent dyes to choosefrom, there are wide choices of individual dye properties within anygiven class. The absorption maxima and reduction potentials ofindividual dyes can be varied through the choice of substituents. As theconjugation forming the chromophore of the dye is increased theabsorption maximum of a dye can be shifted bathochromically.

Emission maxima are bathochromic to the absorption maxima.

Although the degree of bathochromic shifting can vary as a function ofthe dye class, usually the wavelength of maximum emission is from 25 to125 nm bathochromically shifted as compared to the wavelength of maximumabsorption. Thus, dyes which exhibit absorption maxima in the nearultraviolet in almost all cases exhibit maximum emissions in the blueportion of the spectrum. Dyes which exhibit absorption maxima in theblue portion of the spectrum exhibit emission maxima in the greenportion of the spectrum, and, similarly, dyes with absorption maxima inthe red portion of the spectra tend to exhibit emission maxima in thenear infrared portion

A further class of fluorescent compounds which can be used arefluorescent dyes having a chromophoric unit containing at least 5 fusedcarbocyclic aromatic rings (hereinafter referred to as apentacarbocyclic aromatic fluorescent dye). Suitable dyes are describedin U.S. Pat. Nos. 5,150,006 and 5,405,709.

These pentacarbocyclic aromatic fluorescent dyes have been discovered tobe highly advantageous for reducing the wavelength of organic EL deviceemission. To function in a first category arrangement it is essentialthat the fluorescent dye absorb at a wavelength corresponding to anemission wavelength of the host compound. On the other hand, it isrecognized that all fluorescent dyes emit at a longer wavelength thanthey absorb. Stated another way, a dye cannot emit light of a higherenergy level than its absorbs. The difference between the longestwavelength absorption maxima (hereinafter referred to as the peakabsorption) and the shortest wavelength emission maxima (hereinafterreferred to as the peak emission) of a fluorescent dye is known as itsStokes shift. If the Stokes shift of a fluorescent dye is large, it isdifficult to achieve efficient spectral coupling and still achieve peakemission at a shorter wavelength than that of the EL compound.Pentacarbocyclic aromatic fluorescent dyes are particularly suited forshifting organic EL device emissions to shorter blue wavelengths, sincethey exhibit Stokes shifts of from 80 nm to less than 20 nm,attributable to their relatively rigid chromophoric units. Thus, ahypsochromic shift in organic EL device emission can be realized eventhough the absorption peak of the pentacarbocyclic aromatic fluorescentdye is only 20 nm shorter in wavelength than the emission peak of thecharge carrier compound. Preferred pentacarbocyclic aromatic fluorescentdyes are those that exhibit an absorption peak at wavelengths rangingfrom 100 to 20 nm shorter than the emission peak exhibited by theformula II charge carrier compound.

The pentacarbocyclic aromatic fluorescent dyes contemplated each containat least 5 fuised carbocyclic aromatic rings, which form a cluromophoricunit. Fused aromatic carbocyclic rings in addition to the 5 requiredfused rings do not detract from performance characteristics. Preferredchromophoric units contain a perylene, benzopyrene, benzochrysene,benzonaphthacene, picene, pentaphene, pentacene, hexacene oranthanthrene nucleus, as the entire nucleus or fused with other aromaticrings to complete the nucleus. Typically these dyes contain from 20 to40 ring carbon atoms.

These pentacarbocyclic aromatic rings have the advantage that they canbe deposited by vacuum vapour deposition, similarly as the othercomponents of the organic medium. Since the pentacarbocyclic aromaticrings represent chromophores in and of themselves, it is not necessarythat other ring substituents be present. However, many dyes containingpentacarbocyclic aromatic rings as chromophores are conventional, havingbeen originally prepared for use in solution chemistry and thereforehaving substituents intended to modify solubility and, in someinstances, hue.

When fluorescent pentacarbocyclic aromatic dyes are incorporated in ahost charge acceptor compound, only a small amount of the fluorescentdye is required to realize advantages. Fluorescent pentacarbocyclicaromatic dyes are preferably incorporated in a concentration rangingfrom 0.05 to 5 mole percent, based on the moles of charge acceptingcompound. A specifically preferred concentration range is from 0.2 to 3mole percent, based on the moles of charge accepting compound, with aconcentration range of from 0.5 to 2 mole percent, based on the moles ofcharge accepting compound, being in most instances optimum.

A device according to one embodiment of the invention is shown in FIG.17 the accompanying drawing which shows schematically a structure of theinvention and in which there is a aluminium cathode (1), on which thereis a layer of a electron transporting material (2), a layer of a rareearth chelate electroluminescent material incorporating a fluorescentdye (3), a layer of a hole transmitting material (4) and an anode whichis a transparent ITO layer (5). When an electric field is appliedbetween the substrate and the ITO light is emitted via (5).

1-28. (canceled)
 29. An organic electroluminescent device comprising insequence, an anode, a layer of an electroluminescent material, and acathode, in which the electroluminescent material is selected fromcompounds of the general chemical formula

where Lα is selected from organic ligands and from compounds of formula:

where R₁, R₂ and R₃ can be the same or different and are selected fromhydrogen, and substituted and unsubstituted hydrocarbyl groups,substituted and unsubstituted aliphatic groups, substituted andunsubstituted aromatic, heterocyclic and polycyclic ring structures,fluorocarbons, trifluoryl methyl groups, halogens and thiophenyl groups;R₁, R₂ and R₃ can also form substituted and unsubstituted fusedaromatic, heterocyclic and polycyclic ring structures and can becopolymerisable with a monomer; X is Se, S or O; Y is selected fromhydrogen, substituted or unsubstituted hydrocarbyl groups, substitutedand unsubstituted aromatic, heterocyclic and polycyclic ring structures,fluorine, fluorocarbons such as trifluoryl methyl groups, halogens,thiophenyl groups and nitrile and the ligands Lf and Lα are the same ordifferent; Lp is a neutral organic ligand, or is of formula

where each Ph which can be the same or different and can be a phenyl(OPNP) or a substituted phenyl group, other substituted or unsubstitutedaromatic group, a substituted or unsubstituted heterocyclic orpolycyclic group, a substituted or unsubstituted fused aromatic groupsuch as a naphthyl, anthracene, phenanthrene or pyrene group; M and M₁are a rare earth, transition metal, lanthanide or an actinide, M₂ is anon rare earth rare earth, transition metal, lanthanide or an actinidemetal and n is the combined valence state of M, M₁ and M₂ or fromcompounds of the general chemical formula

where L is a bridging ligand and where M₁ and M₃ are selected from arare earth, transition metal, lanthanide or an actinide, M₂ is a nonrare earth metals and M₄ is M₁; Lm, Lp and Ln are the same or differentorganic ligands or are Lα, as defmned above, x is the valence state ofM₁, y is the valence state of M₂, and z is the valence state of M₃ andin which the rare earth metals and the non rare earth metals can bejoined together by a metal to metal bond and/or via an intermediatebridging atom, ligand or molecular group or in which there are more thanthree metals joined by metal to metal bonds and/or via intermediateligands and there is located in the electroluminescent layer as afluorescent material a dye capable of emitting light in response tohole-electron recombination.
 30. An electroluminescent device accordingto claim 29 in which M₂ is selected from lithium, sodium, potassium,rubidium, caesium, beryllium, magnesium, calcium, strontium, barium,copper (I), copper (II), silver, gold, zinc, cadmium, boron, aluminium,gallium, indium, germanium, tin (II), tin (IV), antimony (II), antimony(IV), lead (II), lead (IV) and metals of the first, second and thirdgroups of transition metals in different valence states, manganese,iron, ruthenium, osmium, cobalt, nickel, palladium(II), palladium(IV),platinum(II), platinum(IV), cadmium, chromium. titanium, vanadium,zirconium, tantulum, molybdenum, rhodium, iridium, titanium, niobium,scandium and yttrium.
 31. An electroluminescent device according toclaim 29 in which there is an organic hole transporting material incontact with or mixed with the layer of the electroluminescent material.32. An electroluminescent device according to claim 31 in which the holetransmitting material is a film of a polymer selected frompoly(vinylcarbazole),N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine(TPD),polyaniline, substituted polyanilines, polythiophenes, substitutedpolythiophenes, polysilanes, substituted polysilanes, compounds offormula

where n is from 1 to
 20. 33. An electroluminescent device according toclaim 29 in which there is a layer of an electron transmitting materialbetween the cathode and the electroluminescent material layer or mixedwith the electroluminescent material.
 34. An electroluminescent deviceaccording to claim 33 in which the electron transmitting material is ametal quinolate, an aluminium quinolate or lithium quinolate,cyanoanthracenes such as 9,10 dicyanoanthracenes, polystyrenesulphonates.
 35. An electroluminescent device according to claim 29 inwhich the cathode is selected from aluminium, calcium, lithium,silver/magnesium alloys.
 36. An electroluminescent device according toclaim 31 in which the cathode is selected from aluminium, calcium,lithium, silver/magnesium alloys.
 37. An electroluminescent deviceaccording to claim 34 in which the cathode is selected from aluminium,calcium, lithium, silver/magnesium alloys.
 38. An electroluminescentdevice according to claim 29 in which the fluorescent material is a dyewhich has a bandgap no greater than that of the electroluminescentmaterial and a reduction potential less negative than that of theelectroluminescent material.
 39. An electroluminescent device accordingto claim 29 in which the electroluminescent material is capable ofemitting light of a first wavelength in the absence of said fluorescentmaterial and said fluorescent material is capable of absorbing light atthe first wavelength.
 40. An electroluminescent device according toclaim 38 in which the fluorescent material is a blue emitting dye. 41.An electroluminescent device according to claim 38 in which thefluorescent material is a dye which exhibits a shorter wavelengthemission peak than the electroluminescent material.
 42. Anelectroluminescent device according to claim 29 in which the fluorescentmaterial is a dye which is present in the layer of theelectroluminescent material in a concentration ranging from about 0.05to 5 mole percent.
 43. An electroluminescent device according to claim38 in which the fluorescent material is a dye which is present in thelayer of the electroluminescent material in a concentration ranging fromabout 0.05 to 5 mole percent.
 44. An organic electroluminescent devicecomprising in sequence, an anode, a layer of a hole transportingmaterial, a layer of an electroluminescent material, a layer of anelectron transmitting material, and a cathode, in which theelectroluminescent material is selected from compounds of the generalchemical formula

where Lα is selected from organic ligands and from compounds offormula:—

where R₁, R₂ and R₃ can be the same or different and are selected fromhydrogen, and substituted and unsubstituted hydrocarbyl groups,substituted and unsubstituted aliphatic groups, substituted andunsubstituted aromatic, heterocyclic and polycyclic ring structures,fluorocarbons, trifluoryl methyl groups, halogens and thiophenyl groups;R₁, R₂ and R₃ can also form substituted and unsubstituted fusedaromatic, heterocyclic and polycyclic ring structures and can becopolymerisable with a monomer; X is Se, S or O; Y is selected fromhydrogen, substituted or unsubstituted hydrocarbyl groups, substitutedand unsubstituted aromatic, heterocyclic and polycyclic ring structures,fluorine, fluorocarbons such as trifluoryl methyl groups, halogens,thiophenyl groups and nitrile and the ligands Ln and Lα are the same ordifferent; Lp is a neutral organic ligand, or is of formula

where each Ph which can be the same or different and can be a phenyl(OPNP) or a substituted phenyl group, other substituted or unsubstitutedaromatic group, a substituted or unsubstituted heterocyclic orpolycyclic group, a substituted or unsubstituted fused aromatic groupsuch as a naphthyl, anthracene, phenanthrene or pyrene group; M and M₁are a rare earth, transition metal, lanthanide or an actinide, M₂ is anon rare earth rare earth, transition metal, lanthanide or an actinidemetal and n is the combined valence state of M, M₁ and M₂ or fromcompounds of the general chemical formula

where L is a bridging ligand and where M₁ and M₃ are selected from arare earth, transition metal, lanthanide or an actinide, M₂ is a nonrare earth metals and M₄ is M₁; Lm, Lp and Ln are the same or differentorganic ligands or are Lα, as defined above, x is the valence state ofM₁, y is the valence state of M₂, and z is the valence state of M₃ andin which the rare earth metals and the non rare earth metals can bejoined together by a metal to metal bond and/or via an intermediatebridging atom, ligand or molecular group or in which there are more thanthree metals joined by metal to metal bonds and/or via intermediateligands and there is located in the electroluminescent layer as afluorescent material a dye capable of emitting light in response tohole-electron recombination.
 45. An electroluminescent device accordingto claim 44 in which the fluorescent material is a dye which is selectedfrom the group consisting of coumarin, dicyanomethylenepyrans andthiopyrans, polymethine, oxabenzanthracene, xanthene, pyrylium andthiapyrylium, carbostyril, and perylene fluorescent dyes.
 46. Anelectroluminescent device according to claim 44 in which theelectroluminescent material is capable of emitting light of a firstwavelength in the absence of said fluorescent material and saidfluorescent material is capable of absorbing light at the firstwavelength.
 47. An electroluminescent device according to claim 46 inwhich the fluorescent material is a dye which is a blue emitting dye.48. An electroluminescent device according to claim 44 in which thefluorescent material is a dye which exhibits a shorter wavelengthemission peak than the electroluminescent material.
 49. Anelectroluminescent device according to claim 44 in which the fluorescentmaterial is a dye which is present in the layer of theelectroluminescent material in a concentration ranging from about 0.05to 5 mole percent.